Modern exhaust systems for internal combustion engines carry out relatively complex exhaust gas treatments, wherein different exhaust gas treatment means are used. For example, an oxidation catalytic converter is used to react unburnt hydrocarbons with residual oxygen. Carbon monoxide can also be reacted into carbon dioxide. Further, a particle filter may be provided, especially in case of a diesel engine, to filter out particles carried in the exhaust gas, especially soot. Furthermore, an SCR system, where SCR means Selective Catalytic Reduction, may be provided, preferably in case of a diesel engine. Such an SCR system usually comprises an injector for injecting a reducing agent as well as an SCR catalytic converter. Ammonia or an aqueous urea solution is usually used as the reducing agent. Ammonia can be generated from aqueous urea by means of thermolysis and hydrolysis, and this ammonia can be used in the SCR catalytic converter to reduce nitrogen oxides to nitrogen and carbon dioxide. In order for the reducing agent, which is usually injected in the liquid form into the exhaust gas flow, to be able to evaporate by the time it reaches the SCR catalytic converter and mix with the exhaust gas, a certain mixing section is necessary. To improve the evaporation and/or mixing and to shorten such a mixing section, a static mixer-evaporator may be used, which is to be arranged between the injector and the SCR catalytic converter. Such a mixer-evaporator differs from a conventional static mixer in that the guide surfaces or guide blades of the mixer-evaporator are used at the same time to evaporate liquid reducing agent impinging on them. In particular, such a mixer-evaporator can be made extensively opaque in the direction in which the flow moves through it, so that droplets being carried in the flow can reach the guide blades and evaporated thereon. Such a mixer-evaporator is consequently always to be arranged downstream of an injection, which is provided for injecting the liquid reducing agent, in an SCR system, which operates with a liquid reducing agent.
In addition, the fact that only a comparatively small space is available for installation for accommodating the exhaust system arises as a general problem in case of applications in vehicles.